Collapsible tubes are well known in the art. They are used, for example, as dispensers for toothpaste and shampoo. They are also commonly referred to as squeeze tubes. In forming a collapsible tube of this type, the body or sidewall portion is formed separately from the headpiece portion. The headpiece, generally, is molded to the formed sidewall portion.
One commonly employed sidewall is a multi-ply, collapsible sheet material having inner and outer plastic plies, usually polyethylene, and an inner metal foil ply, usually aluminum. The aluminum acts as a barrier to oxygen penetration and flavorant migration. The polyethylene protects the aluminum from the contents of the tube, provides a convenient printing surface and affects the feel of the tube to the end user. The aluminum and polyethylene are combined in amounts that provide a desired collapsibility and avoidance of spring back. All of this is known in art and will not be gone into further herein because the structure of the sidewall does not form a part of this invention except that the headpiece must be bondable to the sidewall.
The headpiece of the tube provides a number of functions. Because it forms one end of the collapsible tube, it, obviously, must have a degree of structural integrity to prevent collapse in use. In addition, it must be formed of a material which, like the materials in the sidewall, prevents migration of the substance of the contents or deterioration of the contents. Further, the material of the headpiece has to be bonded to the plastic material of the sidewall and it must resist corrosion from the contents of the tube as well as avoid chemically reacting with the contents of the tube. Where the tube contents are such that these functions cannot be provided by the same plastic material, the prior art has attempted to provide other solutions. For example, as shown in U.S. Pat. No. 3,260,411, a barrier member is provided within the headpiece, adjacent the contents of the tube. This prevents the migration or deterioration of the substances held within the tube.
However, the cost of separately forming and inserting this barrier member is high, so that its use is uneconomic. Further, there is a problem in holding the barrier member to the rest of the tube.
It is an object of the present invention to provide a headpiece which allows both the structural integrity and the protection of the contents without the necessity for an additional insert.
It is a further object of the present invention to provide a method for forming an integral headpiece of two plastic materials in an expeditious and efficient manner.
It is a still further object to provide an extrusion die for use in forming an integral headpiece of two thermo-plastic materials.
Because of the very high volume with which these tubes are used, any saving in the cost per tube will amount to a significant total figure. Furthermore, the cost of the tube is often an appreciable fraction of the cost of the goods contained therein and thus it is important that the cost of the tube be minimized. One of the key considerations in keeping the cost of the tube to a minimum is to fabricate the tube on a high speed machine whose design is sufficiently simple and trouble free so that there is minimum downtime for repairs and adjustments.
Accordingly, it is a further purpose of this invention to provide equipment which will mold a headpiece onto a cylindrical sidewall, which equipment is capable of high speed operation with minimum downtime for repairs and adjustments.
Related to this purpose is the object of providing headpiece molding machinery which has a minimum of moving parts and in which complex movements are avoided as much as possible.